Emmetropization is the regulatory process that matches the eye's length to its optical power, bringing distant objects to focus on the retina with accommodation relaxed. Myopia, or shortsightedness, is the failure of emmetropization in which the eye grows too long for its optical power. Myopia's association with sight-threatening complications, and near-epidemic prevalence in several populations, make it critical to understand the determinants of emmetropization, without which effective treatments are unlikely to be developed. The chick eye has provided a very fruitful model of emmetropization, clarifying the optical conditions that lead to myopia, providing evidence for local retinal control of eye growth, and identifying optical manipulations that inhibit eye elongation, which are therefore potential myopia treatments. Aims and Studies: (1) We will study local molecular signaling across the retinal pigment epithelium (RPE), which separates the image-processing retina from the choroid and eye shape-determining sclera, using molecular techniques to delineate patterns of gene expression in eyes undergoing experimentally altered growth through exposure to myopic and hyperopic defocus, and in cultured RPE treated with presumptive retinal growth modulators. We will then conduct in vivo tests of growth factors identified in gene expression studies. (2) We will use these genetic signatures, in combination with drugs known from previous work to modulate responses to imposed myopia and hyperopia, to study the mechanisms of eye growth induced by simultaneous, competing myopic and hyperopic defocus produced by several types of multifocal and astigmatic lenses. We will evaluate hypotheses regarding retinal processing, optical aberrations, and peripheral retinal growth to explain lens effects. (3) We will develop a guinea pig model to extend our findings on local ocular growth regulation to mammalian eyes, and to compare mammalian and avian responses to simple and competing defocus stimuli. PUBLIC HEALTH RELEVANCE Emmetropization is the regulatory process that matches the eye's length to its optical power, bringing distant objects to focus on the retina with accommodation relaxed. Myopia, or shortsightedness, represents the failure of emmetropization in which the eye grows too long for its optical power, in near-epidemic prevalence in several populations, with associated sight-threatening complications, making it critical to understand the determinants of emmetropization, without which effective treatments are unlikely to be developed. This project will apply modern molecular biology and optical techniques to investigate the mechanisms underlying emmetropization, with a view to developing novel treatments for myopia.